Lignin is a wood-derived polyphenol polymer that is produced as a by-product from the kraft wood pulping process. Typically, “black liquor” obtained from the kraft process is separated from the remaining wood pulp and then kraft lignin is isolated from the black liquor by any number of methods. Kraft lignin is a macromolecule comprising a variety of functional groups, including phenol, methoxy, ether, and alcohol moieties. Kraft lignin has found use in adhesive mixtures for engineered wood materials. Powdered lignin, e.g., kraft lignin, however, is an explosive compound at moisture contents of less than 10 wt %, making powdered lignin dangerous to handle and prepare.
Powdered or particulate, curable aldehyde based resins, e.g., phenol-formaldehyde (PF) resins, have found wide use as an adhesive for a variety of lignocellulose composite products such as oriented strand board (OSB) and other wafer or chip board products. Reaction products produced by the reaction of lignin and PF resins have also been tested as adhesives for similar wood composite products. The commercial use of low-moisture content lignin, however, is limited by the explosive properties as described above.
There is a need, therefore, for compositions that include one or more powdered lignins having a moisture content of less than 10 wt % that are stable for handling, processing, and/or transport.